System of Government in USA

USA has presidential system of government in which the president is directly elected by the people of United States of America. There are presidential elections after every four years in USA. A president is elected for a period of 4 years. He can retain the office for a maximum period of two tenures which makes it 8 years provided if the people of USA elects the same person for the second time.
There are political parties which participate in the electoral system. One is the democrats while the other is the republicans. President Obama is from the Republicans party while bush was from the democrats. There is a vice president in USA which acts as president in his absence. Similarly all the States have their own Governors which are elected by the citizens of those States directly.
There are two houses of parliament in USA. The lower house is named as congress while the upper house is named as the Senate. The runner up in the presidential elections become the senator. The country is following democracy in its true spirit.